<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>bind练习</title>
</head>
<body>
    <button>点我</button>
    <script>
        var btn = document.querySelector('button');
        btn.onclick = function(){
            console.log(this);
            // var that = this;
            // setTimeout(function(){
                console.log(that);
            //     console.log(this);
            // }.bind(this),2000);

            var fn = function(){
                console.log(this);
            }.bind(this);
            //fn.call()  fn()
            window.setTimeout(fn,2000);
        }
    </script>
</body>
</html>